The present invention relates to a device for locking wheel rims for vehicles on repair workshop machines, particularly tire-changing machines or the like.
The use is known of so-called tire-changing machines which allow fitting and removing tires onto and off the relative rim of a vehicle wheel, e.g., for carrying out maintenance jobs or replacing the rim and/or the tire itself. Such tire-changing machines generally consist of a base structure supporting a chuck for gripping and rotating the rim of a wheel and of at least a tool bearing arm having one or more tools suitable for removing and/or fitting the tire from and onto the rim.
Different known types of chucks exist. A first type consists of a fastening plate for the rim, which is fitted on the base structure of the tire-changing machine in a rotatable way around a central work axis and which has four rim gripping clamps. The clamps move from the center towards the outside of the plate and vice versa, between a closing configuration, corresponding to the positioning of the clamps at the centre of the plate, and an opening configuration, corresponding to the positioning of the clamps at the edge of the plate. Such type of chuck is not without drawbacks. In particular, the clamps are subject to breakage and the actuators for moving the clamps themselves are subject to faults.
A second type of chuck comprises a resting plate for the rim, which is fitted on the base structure of the tire-changing machine in a way rotatable around a central work axis and which has a threaded hole inside which a rim lock pin can be fitted and screwed.
The lock pin has a thread along its entire length and has, in particular, an extremal portion that can be fitted and screwed inside the hole on the resting plate, through the central hole passing through the rim, and a grip handle opposite such extremal portion.
A lock cone is coupled to the pin in an axially rotatable manner. The lock cone has suitable grip knobs, suitable for engaging on the rim in correspondence to the central hole passing through the retention of the rim itself on the resting plate.
During use, the rim is positioned on the resting plate, with the central hole of the rim aligned with the threaded hole on the plate. The above extremal portion of the pin is screwed inside the hole on the plate, until the cone is positioned in contact or in any case in the proximity of the rim, above this. The screwing up of the cone on the pin, done by means of the knobs, allows positioning the cone itself in contact with the rim, inside the through hole, and therefore allows locking the rim on the resting plate.
Once the rim has been locked on the retention plate, this is caused to rotate around the central work axis. This type of chuck does however have a number of drawbacks. In particular, the action of locking the rim on the resting plate must be done manually, by screwing the cone on the rim itself, with consequent considerable physical effort on the part of the operator.
To overcome this problem, a further type of chuck is known comprising an actuator cylinder suitable for moving the pin, and therefore the cone screwed onto it, towards the rim, to lock this on the resting plate. Also this type of chuck does however have a number of drawbacks. For effective locking during all fitting/removal operations performed on the wheel in fact, a considerable force must be applied to the rim and, consequently, the use is required of an actuator cylinder of considerable dimensions. This consequently means the chuck takes up a fairly large amount of room, and that the means provided to make the chuck itself rotate during the fitting/removal operations on the wheel are more complex.